The present invention relates to electric generator assemblies for projectiles; and more particularly to assemblies including turbine-driven electrical generators adapted to power electrical sensing and control apparatus in projectiles such as artillery shells, rockets, and the like.
Military applications provide a constant and strong demand for new electronic technology. One aspect of this demand has been the application of electronic technology to military ordnance. Increasingly, projectiles have been equipped with sophisticated electronic sensing and control devices. These devices share a common requirement: A reliable, inexpensive source of electric power to operate them.
In the past, electrical devices associated with projectiles such as proximity and timing fuzes have often been powered by storage batteries. However, a number of problems are associated with the use of storage batteries. For example, storage battery-equipped fuzes, like other types of military hardware, must be designed to be stored for long periods of time prior to use in order to minimize logistic costs, and yet be instantly available for use when necessary. Dry cell batteries have limited useful lives. Wet cell batteries are used such that the electrolytic fluid is injected automatically into the electrodes, as a result of shell spin after leaving the gun. Batteries may not be stored separately from the electrical portion of the fuze which they are to power, but must be preassembled with the fuzes, for logistic and "ready available" reasons. Thus, the batteries or battery-equipped fuzes must be assembled into the projectiles before the ordnance can be used. Some types of battery-equipped fuzes have proven very unreliable, as a result of electrolyte fluid leakage.
An alternative source of electrical power for projectiles is the air turbine-driven electric generator. Compared with batteries, generators have the advantage of unlimited storage lives. However, prior art electrical generators driven by air turbines suffer from a number of disadvantages. Generally, they are expensive to manufacture. Further, the impellers used in prior art generators are generally very inefficient in that most of the air taken in by the turbine is diverted rather than used to drive the impeller. Typically, an air intake is provided in the nose of the projectile in which the generator is mounted. The large air volume required by prior art generators substantially alters the aerodynamic characteristics of the projectile, resulting in altered trajectories and firing ranges. The large volume required also makes the projectile performance characteristics more sensitive to atmospheric conditions such as barometric pressure and precipitation than are projectiles having battery powered electrical equipment.
Prior art turbines typically operate at very high angular velocities which may range well over 100,000 RPM. Consequently, the dynamic balance of the generator must be precise, requiring the use of expensive ball bearings and other precision parts. Further, because the rate of rotation of the turbine depends on the projectile's velocity, the frequency of the generator's output varies over the course of the projectile's trajectory. Thus, the electrical current generated may require conditioning before it can be used to power some types of frequency-sensitive devices.
When used in projectiles, air turbine-driven generators experience substantial acceleration forces in the barrel from which the projectile is fired. Prior art generators which require precision axial thrust bearings to achieve and maintain high angular velocities during the projectile's trajectory have an unacceptably high failure rate because the precision bearings tend to be damaged when the projectile is fired.
Thus, there is a need for a source of electrical power for the electrical equipment associated with modern day projectiles which is inexpensive, reliable, and readily available without the extra processing steps associated with activation of some types of storage batteries and which overcomes the problems associated with presently available air turbine-driven generators. The present invention meets these needs and has other advantages as described below.